The present invention generally relates to a fan impeller for use in an air conditioner or the like, and more particularly, to airfoil blades for a fan impeller, and also manufacturing method thereof.
It has been a recent trend that airfoil blades have been employed not only for large-sized blowers, but also for blowers in domestic use as well, for the purpose of improving performance of such blowers.
Conventionally, for manufacturing such airfoil blades, it has been so arranged, for example, as shown in FIG. 3, that a blade 14 of a generally hollow structure fundamentally includes an inner frame having a plurality of ribs 20 and 26 provided to be arranged from a leading edge to a trailing edge of the blade 14, and an upper surface wall 28 and a lower surface wall 30 applied onto the inner frame to provide a surface wall assembly, thereby forming a desired airfoil section as illustrated.
The leading edges or nose portion of the upper and lower surface walls 28 and 30 are welded to a solid rod 32, while the trailing edges thereof are also welded to a rib 34 with a relatively narrow width, provided at the rear end portion. Furthermore, as is shown in FIG. 3, an outer liner including an upper surface liner 42 and a lower surface liner 44 is placed in relation to be overlapped with the upper and lower surface walls 28 and 30, and is fixed thereat by screwed upset type coupling members, etc. (not particularly shown).
For the above airfoil blade, the liners 42 and 44 of a corrosion resisting alloy are employed for protection against corrosion, and in order to combine the liners 42 and 44 with the surface walls 28 and 30, a novel coupling device employing upset type coupling members having metallic portions not projecting from the blade surface is employed to manufacture a blade which will not obstruct smooth air flow over the surface of the airfoil blade, as disclosed, for example, in Japanese Utility Model Publication Jikkosho No. 60-12959.
Meanwhile, as another prior art, there is also proposed an airfoil blade as shown in FIG. 4, which includes a hollow and thin-walled main body B having an external sectional shape and a plurality of screw setting portions F integrally formed within the main body B in a state as combined with said main body by extrusion molding. Openings 0 are necessarily formed during extrusion molding by core support portions to form female screwed holes Fa for set screws at the center of the respective screw setting portions F, and these openings 0 are directed towards the rear portion Ba of the main body B as disclosed, for example, in Japanese Utility Model Publication Jikkosho No. 62-14397.
In the airfoil blade as described above, since the openings 0 are arranged to be directed towards the rear portion Ba at which centrifugal force and air resistance are not exerted upon rotation of the fan impeller, a rigid assembly may be effected.
In the construction of the former prior art referred to above, many man-hours are required for the manufacture of the blade, thus undesirably resulting in cost increase, while strain, detachment, etc. at the welded portions tends to take place. Moreover, the upper or lower surface wall for the airfoil blade has a limitation in its thickness for making holes therein and effecting tapping to receive set screws.
Meanwhile, in the latter conventional arrangement, although the extrusion molding is possible for the blade of a two-dimensional curved surface, such molding becomes impossible for the blade of a complicated three-dimensional curved surface having distribution also in a radial direction of the fan impeller.